This invention relates to water-in-oil emulsion polymerization processes and to the water-in-oil emulsions prepared therefrom.
Various water-soluble polymers such as polyacrylamide and copolymers of acrylamide with other anionic, cationic or nonionic monomers are well-known to be precipitants or flocculants for many substrates including sewage, cellulosic fibers and fines for retention and freeness, effluent waste for metal production, coal tailings and the like. Such polymers are also known to exhibit superior thickening properties when said polymers are dissolved in aqueous media. Particularly well-known for this purpose are the anionic polyacrylamides such as acrylamide/acrylic acid copolymers, including those prepared by hydrolysis of polyacrylamide. Such polymers are also very useful as fluid mobility control agents in enhanced oil recovery processes.
In the past, such polymers have been made available commercially as powders or finely divided solids which must be subsequently dissolved in an aqueous medium in order to be used. Because such dissolution steps are sometimes time consuming and often require rather expensive mixing equipment, it has become a common practice to formulate the water-soluble polymers in water-in-oil emulsions wherein the polymer is dissolved in the dispersed aqueous phase. Such emulsions, as well as methods for preparing them, are described in U.S. Pat. No. 3,284,393 to Vanderhoff et al. In order to accelerate the inversion (i.e., solubilization) rate of such emulsions, it has been a common practice, for example, as shown in U.S. Pat. No. RE 28,474, to add a water-soluble surfactant to the emulsion during or just prior to inversion. While the foregoing procedures generally do overcome the problems of dissolving dry powders of water-soluble polymers in aqueous media, such emulsions contain substantial quantities of water and oil, thus increasing the cost of manufacturing, shipping and handling such polymers to a significant degree. In addition, the stability of such emulsions after storage for significant periods is often very poor.
In an attempt to employ less quantities of water and oil in said emulsion, it is taught in U.S. Pat. No. 4,052,353 to concentrate such emulsions by removing water from the emulsions and subsequently adding sufficient water-soluble surfactant to render the water-soluble polymer self-dissolving in water. Unfortunately, however, the stability of such emulsions after storage for significant periods is not as high as is desirable. Other attempts to employ less quantities of oil in said emulsions have been made by decreasing the oil phase of said emulsions while holding the polymer-water phase constant, as taught in U.S. Pat. No. 3,826,771. Unfortunately, the bulk viscosity of said emulsions increases severely, and limits such attempts to concentrate conventional emulsions.
In view of the foregoing deficiencies of conventional emulsions and concentrated dispersions derived from such emulsions, it is highly desirable to provide a water-in-oil emulsion of a water-soluble polymer that can be inverted quickly into an aqueous medium, can be stored for substantial periods of time without losing stability, contains a high polymer content, and yet exhibits a low bulk viscosity.